If the exposure rate at 10 m from a source is 20 mR/h, what would it be at 5 m after two half-lives?

To determine the exposure rate at 5 meters after two half-lives, we first need to address the concept of half-lives in radiation. A half-life is the time required for a quantity to reduce to half its initial value. After two half-lives, the exposure rate from the source will be reduced to one-fourth of its initial level.

Starting with the exposure rate of 20 mR/h at a distance of 10 meters, after two half-lives, the new exposure rate would be calculated by taking the initial rate and applying the reduction:

1. After the first half-life, the exposure rate would be 20 mR/h / 2 = 10 mR/h.

2. After the second half-life, the exposure rate would be 10 mR/h / 2 = 5 mR/h.

Next, to find the exposure rate at a distance of 5 meters, we must account for the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. Since we are moving from 10 meters to 5 meters, the distance decreases, causing the exposure rate to increase.

From 10 meters to 5 meters, the distances